It's because it's not written in QBasic. It's written in a variant of QBasic called QB64 [1] - a spiritual successor to Microsoft's QBasic intended to run on modern 64-bit machines.
I went over the BAS source the last time this was posted a few weeks back and it has a lot of keywords that are specific to QB64 so unfortunately you can't run this on a true DOS machine (or DosBox).
The first time it barfed was because there was a space in the filename, and the QB64 editor didn't handle it. Running on the command line, with quotes around the name, was flawless.
I did give it a try, but no luck; qb64 seems to only run the code by compiling it via C++, and that failed on my system. (And I don't have the determination to try to find out why.)
I went over the BAS source the last time this was posted a few weeks back and it has a lot of keywords that are specific to QB64 so unfortunately you can't run this on a true DOS machine (or DosBox).
[1] https://qb64.com